This invention relates to an apparatus for the analysis of the resultant force at a joint in a human or animal body.
Recently, in the field of orthopedic surgery or other similar branches of medicine, there has been frequently felt the necessity of analyzing the resultant force at a joint. In the case of a patient whose hip joint has been replaced with an artificial joint, for example, if the value of the resultant force at the artificial joint calculated after the surgery exceeds 3.5 times the body weight of the patient, the joint will be deficient in load bearing capacity so that the joint will, more often than not, be unable to recover its normal function. For this reason, it is quite important from the clinical point of view to analyze the magnitude and direction the resultant force exerts at the joint before and after the surgery for total joint replacement. The resultant force at the joint has heretofore been determined by use of a pedestrian analyzer or by a method which utilizes a transducer inserted in the patient's body and a telemeter installed separately to receive and analyze data from the transducer. These devices are invariably expensive and cannot be easily operated because they involve highly advanced electronic technology. Under the circumstances, clinical practitioners specializing in orthopedic surgery are compelled to reckon the resultant forces at the joints on the basis of figures drawn from X-ray images of the joints. Generally it is difficult to insert lines on the X-ray films, and an effort to print a new X-ray picture and draw figures from the X-ray picture entails a great deal of work. Another possible method involves the drawing of an X-ray image on a monitor with a light pen. The actual operation of this method, however, requires use of an expensive image analyzer.
A primary object of this invention, therefore, is to provide an analyzer for the resultant force at a joint, which is inexpensive and can be easily operated by any person, skilled or unskilled.